This invention relates to a harness assembly for a nasal mask.
The invention will be described with reference to a harness assembly for a nasal mask fitted to the head of a wearer for communicating breathable gas to a patient""s airways, for example in the administering of continuous positive airway pressure (CPAP) treatment. However, the invention is not limited to this particular field of use and is equally suited for masks used in assisted respiration or mechanical ventilation.
CPAP treatment is administered when a person is asleep It is therefore crucial that nasal CPAP masks be securely fastened to the wearer""s head. Leaks occurring due to mask movement caused by gross body motion during sleep can result in the efficacy of CPAP treatment being defeated. An effective seal of the mask cushion to the patient""s face is, in part, a function of the mask design, and is also a function of the correct tension in the harness being maintained. Under-tensioning results in a loose mask and poor seal. Over-tensioning can lead to discomfort for the wearer. All of these problems can lead to patient non-compliance.
A prior art nasal mask and harness arrangement is taught in U.S. Pat. No. 5,243,971 assigned to the University of Sydney. The nasal mask is secured to a wearer""s head by a harness comprised of an upper strap and a lower strap, each of which is secured to a frame of the nasal mask. The upper portion of the frame includes a pad that engages the wearer""s forehead. The frame further carries a nasal cushion that, in use of the mask, sealingly engages the wearer""s nose and face. The frame also carries a mask body to which is connected a flexible conduit for the delivery of breathable gas to the mask and thereafter to an entrance to the patient""s airway.
A problem with this arrangement is that the upper and lower straps are made from an elastic or resilient material which lose elasticity with time and become loose fitting about the wearer""s head. Furthermore, movement of the wearer during sleep, may cause sliding movement of the straps to the point where the mask can become loose and leaks occur.
Also, the tightening of either the upper or lower strap tends to pivot the mask thereby altering the tension of the other strap making comfortable and correct adjustment difficult and time consuming.
Other harness arrangements, such as that shown in U.S. Pat. No. 5,542,128 in the name of Lomas, include an upper strap around the head and a lower strap around the neck. This arrangement exacerbates the tensioning problem discussed above as rocking of the head moves the face relative to the neck thereby altering the tension of the straps, especially the neck strap.
Another prior art arrangement is disclosed in published Australian Patent Application No. 32914/95 in the name of Buckley-Mendez.
It is important to distinguish nasal masks for the administration of CPAP treatment from respirators or breathing apparatus that are characterised by full face is cover and are intended to simultaneously deliver air to the nose and mouth of a conscious and mobile patient. In contrast, CPAP treatment primarily occurs during sleep when the wearer of a nasal mask is mostly immobile and cannot tolerate the discomfort of respirators or breathing apparatus for want of arousing from the sleep state.
The present invention is directed to overcoming, or at least ameliorating, one or more of the disadvantages of the prior art.
Accordingly, in a first aspect, the present invention provides a harness assembly for a nasal mask for communicating breathable gas to a patient""s airways, the harness assembly includes a cap portion adapted to engage, in use, the occipital region of the skull, said cap portion including a connection means at each end, and a pair of upper and lower straps, each of the straps extending between one of the cap connection means and the nasal mask.
The harness assembly according to the invention grips the head in a region substantially fixed relative to the face and, as such, strap tension is not substantially affected by head movement.
Preferably, the cap connection means are adapted to allow the cap portion to pivot substantially independently of the mask and straps.
The connection means are desirably disposed, in use, adjacent the ears of the wearer. Most desirably, they are just above the ears.
The cap connection means are preferably further adapted to allow each strap to move substantially independently of the other straps.
Each strap is preferably length adjustable.
Desirably, the cap portion, in use, covers the occiput of the wearer.
In an embodiment, the cap portion engages and/or grips the curved region of the occiput.
In another embodiment, the cap portion includes an opening through which, in use, the occiput at least partially protrudes.
The connection means desirably also allows the straps to slide normally relative to the direction of the strap.
In a particularly preferred embodiment, the connection means are in the form of substantially D-shaped members. In this embodiment, the cap portion is connected to the straight portion of the D-shaped members and the upper and lower straps are each respectively connected to the upper and lower curves of the D-shaped members.
In another preferred embodiment, the connection means is in the form of a triangular member. In this embodiment, the cap ends and the upper and lower straps each respectively engage a side of the triangle.
In another particularly preferred embodiment, the connection means is in the form of a yoke shaped member having a inner bar and a pair of outer bars each angled slightly with respect to the inner bar. In this embodiment, the cap portion is connected to the inner bar and the upper and lower straps are each connected to one of the outer bars.
In yet another embodiment, the connection means are in the form of substantially xe2x80x9cCxe2x80x9d shaped members. In this embodiment the. lower straps connect to the head of the C, the upper straps to the middle and the cap portion to the base. In this embodiment, the cap portion and the upper straps can be manufactured from a single component
The connection means is preferably produced from plastics, elastomers, composites, laminates or other like materials.
The cap portion and straps can be produced from fabric or like materials or laminates thereof. The cap portion may also be moulded to snugly fit the head, in particular to replicate the shape of the occiput, by thermoforming, fabric darting, or joining two or more pieces along a non-straight seam.
In a second aspect, the invention provides a nasal CPAP mask and harness assembly, the assembly includes a mask with a nasal cushion and mask body connected to the harness assembly of the first aspect.